title: Phenotypic heterogeneity in skeletal muscle sodium channelopathies: A case report and literature review.
abstract: Skeletal muscle sodium channelopathies (SMSCs) including hyperkalemic periodic paralysis (HyperPP), paramyotonia congenita (PC), and sodium channel myotonia are caused by sodium channel gene (SCN4A) mutations, with altered sarcolemal excitability, and can present as episodes of skeletal muscle weakness, paralysis, and myotonia. We report a teenage boy, who presented with features of HyperPP, PC, myotonia congenita, and sodium channel myotonia. His electromyography (EMG) revealed myopathic changes, myotonia, and Fournier EMG pattern I, and posed a diagnostic challenge. Genetic analysis showed Thr704Met mutation in SCN4A gene. While with typical clinical phenotypes, the electromyographic patterns can be used to direct genetic testing, atypical phenotypes may pose diagnostic dilemmas. Clinicians dealing with neuromuscular disorders in children need to be aware of the unusual clinical presentations of SMSC, so that focused genetic testing can be carried out.
authors.affiliation: Department of Paediatric Neurology, Leicester Royal Infirmary, University Hospitals of Leicester NHS Trust, Leicester, UK.
authors.forename: Rashid
authors.initials: R
authors.lastname: Saleem
authors.forename: Gururaj
authors.initials: G
authors.lastname: Setty
authors.forename: Arif
authors.initials: A
authors.lastname: Khan
authors.forename: Duncan
authors.initials: D
authors.lastname: Farrell
authors.forename: Nahin
authors.initials: N
authors.lastname: Hussain
keywords: Allelic disorder; myotonia; periodic paralysis; phenotype-genotype protocols; sodium channelopathy